can steam lower the rate of increase in temperature after a certain point below 100 deg. centigrade?

We were doing an experiment in class, where we pumped steam into tubes, to test the effects of thermal expansion. The problem is that the temperature of the tubes quickly increased up to 80 deg. C; afterwards, the increase in temp. became really slow, like 2 deg. per minute. btw, we were using a thermistor to check for the temp.

Anyways, I remember reading that perspiration cools our body using evaporization, so couldn't condensed water inside the tube cause it to absorb the heat instead of the metal taking it.( note that the steam would've turned into water when it released heat towards the tubes). However, we did tilt the tubes so that the water would drain out but could this still be substantial enough to retard the heating process??? If so,, what's the phenomenon called?